Final answer:
In metastatic cancer, tumors spread primarily through the lymphatic system and the cardiovascular system, with the bloodstream playing a key role in transporting cancer cells to form metastases in distinct organs.
Step-by-step explanation:
In metastatic cancer, tumors spread beyond the regional area predominantly through the lymphatic system and the cardiovascular system, namely the blood vessels. Metastasis occurs when cancer cells travel from the primary tumor through the bloodstream to form new cancers, called metastases, at distant sites. Certain types of cancers are known to metastasize to specific organs such as the brain, lungs, bones, and liver. This process is facilitated by the bloodstream and is associated with the worst prognosis due to the cancer spreading throughout the body.